Fix: memory leaks on event notifier destroy

Fix: memory leaks on event notifier destroy

Both filter runtime and event enabler ref objects are owned by the
event notifier, but are not freed upon destruction of the event notifier
object, thus leaking memory.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I511569f56a38f670549a93cb6179b77861245712